Eye viewing device for large field viewing

ABSTRACT

The invention is a low cost, low input power eye viewing device well suited for viewing wide field retinal images through an undilated pupil. Included in the device are a converging light illumination system and an aperture stop. The converging light illumination system provides ease of entry of light rays into an eye, wide field retinal illumination, reduced glare and reduced power consumption. The aperture stop blocks unwanted received glare light not forming part of the retinal image. The device is made especially well suited for retinal viewing through an undilated pupil if the aperture is sized in accordance with the diameter of an undilated pupil.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of application U.S. Ser. No.10/033,557, filed Dec. 27, 2001, entitled Eye Viewing Device for LargeField Viewing, which is a continuation of U.S. Ser. No. 09/444,161,filed Nov. 22, 1999, entitled “Eye Viewing Device for Retinal ViewingThrough Undilated Pupil,” now U.S. Pat. No. 6,409,341 issued Jun. 25,2002, which is a continuation-in-part of U.S. Ser. No. 09/198,545, filedNov. 24, 1998, entitled “Ophthalmoscope Comprising Defocused LightSource,” now U.S. Pat. No. 6,065,837 issued May 23, 2000. The prioritiesof all of the above applications are claimed and all of the aboveapplications are incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates generally to medical diagnosticinstruments, and specifically to an eye viewing device for use in eyeviewing.

[0004] 2. Background of the Prior Art

[0005] Commercially available eye viewing devices for use in retinalviewing have been observed to exhibit numerous limitations.

[0006] According to an indirect ophthalmoscope design, a beam splitteris provided in the optical viewing path which directs illumination lightrays into an eye, and simultaneously allows receive imaging light raysto pass therethrough. The substantial light losses inherent with thisdesign require that a large, high powered light source be incorporatedin the device for the device to satisfactorily illuminate a retina. Highpowered light sources, in general, are difficult to package, consumeexcessive amounts of input power, and produce large amounts of heat andunwanted light such as glare. High powered light sources also have largefilaments, typically larger than the diameter of an undilated pupil.This makes indirect ophthalmoscopes especially susceptible to glareproblems attributable to incident light rays being reflected from outereye structures such as the iris, cornea, and sclera.

[0007] Cameras for retinal imaging, such as fundus cameras, provide highquality imaging. However, retinal viewing cameras, in general, areexpensive, typically require pupil dilation for retinal viewing, andtypically require operation by a highly skilled and trained cameraoperator.

[0008] There is a need for a compact, lower input power eye viewingdevice which provides appropriate retinal illumination and whichfacilitates wide field retinal viewing without requiring pupil dilation.

SUMMARY OF THE INVENTION

[0009] According to its major aspects and broadly stated the presentinvention is a low input power, low cost eye viewing device for use inviewing a retina. The device provides wide field retinal viewing withoutpupil dilation.

[0010] In one aspect, an eye viewing device according to the inventionincludes a converging light illumination system adapted to generatelight rays which, when the device is in an operative position, convergeat about a pupil of a patient and diverge inside an eye to illuminate awide retinal field. The converging light illumination system providesillumination of a wide retinal field through a small pupil which may bein an undilated state. The converging light illumination system alsoreduces electrical input power consumption and reduces glare, assubstantially all light delivered by the illumination system enters aneye through a patient's pupil without being reflected from an eyestructure outside of a pupil opening such as the iris and sclera.

[0011] In another aspect, an eye viewing device of the inventionincludes a viewing system having an aperture stop positionedsubstantially conjugate to a patient's pupil and substantially coaxialwith an imaging axis of the viewing system. An aperture stop positionedsubstantially conjugate to a patient's pupil and substantially coaxialwith an imaging axis operates to admit light that forms a retinal imageand to block light that does not form the retinal image. The aperturestop operates to block unwanted light both when the device is positionedforward of an operative position and when the device is in an operativeposition. The aperture stop thereby reduces glare and improves imagequality both during entry of the device into an eye (when the device isbeing maneuvered into an operative position) and during retinal viewing(when the device is in an operative position).

[0012] The eye viewing device is made especially well suited for retinalviewing through an undilated eye by sizing the aperture of the aperturestop in accordance with the diameter of a pupil of an undilated eye. Bysizing the aperture in accordance with the diameter of an undilatedpupil, the aperture stop operates to block substantially all lightreflected from eye structures outside the diameter of a pupil (such asthe iris and sclera).

[0013] These and other features of the invention will become clear tothose skilled in the art from a careful reading of the DetailedDescription of the Prefered Embodiments in connection wit the referencedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The preferred embodiment of the invention will now be describedby way of example only, with reference to the accompanying figureswherein the elements bear like reference numerals, and wherein:

[0015]FIG. 1A is a functional schematic diagram of an eye viewing devicefo the invention showing illumination light rays for illustratingoperation of an illumination system according to the invention;

[0016]FIG. 1B is a functional schematic diagram of an eye viewing deviceaccording of the invention showing receive optical light rays whichillustrate operation of the devices' imaging system;

[0017]FIG. 1C is a functional schematic diagram of an eye viewing deviceof the invention showing illumination light rays when the device is at adistance away from an operative position;

[0018]FIG. 1D is a functional schematic diagram of an eye viewing deviceof FIG. 1C showing receive optical light rays when the device is at adistance away from an operative position;

[0019]FIG. 1E is a functional diagram of an eye viewing device of theinvention showing incident light rays reflected from an objective lens;

[0020]FIG. 2 is a functional schematic diagram showing incident lightrays of an illumination system which may be incorporated in theinvention;

[0021]FIG. 3A is a functional schematic diagram of an embodiment of theinvention showing light rays from an on-axis object illustratingoperation of an embodiment of an imaging system according to theinvention having a defocused mirror;

[0022]FIG. 3B is a functional schematic diagram of an embodiment of theinvention showing light rays from an off-axis object illustratingoperation of an imaging system according to the invention having adefocused mirror;

[0023]FIG. 3C is a functional schematic diagram of an embodiment of theinvention showing illumination light rays which illustrate operation ofan illumination system having an on-axis light source;

[0024]FIG. 4 is a functional schematic diagram of another embodiment ofthe invention having a defocused light source;

[0025]FIG. 5 is a functional schematic diagram of the inventionconfigured for binocular viewing;

[0026]FIG. 6 is a physical schematic diagram illustrating variousfeatures which may be incorporated in a physical embodiment of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

[0027] An exemplary embodiment of an eye viewing device according to theinvention is described with reference to FIGS. 1A-1E. Eye viewing device10 includes an illumination system, the operation of which is describedmainly with reference to FIG. 1A, and an imaging system, the operationof which is described mainly with reference to FIG. 1B.

[0028] The device of FIGS. 1A-1E is especially well suited for use inviewing a retina through an undilated pupil. Small diameter undilatedpupils present numerous challenges to viewing retinal images. Smalldiameter undilated pupils tend to inhibit the transmission of bothincident light directed toward a retina and reflected lightcorresponding to a retinal image. Furthermore, light that is directedinto a pupil and that is blocked from entry into a pupil by highlyreflective surfaces of outer eye structures such as the iris and scleratends to be reflected into a viewing system as glare. As will beexplained herein below, the device of FIGS. 1A through 1E includesfeatures which operate in combination to overcome the numerouschallenges to viewing a retinal image through an undilated pupil. In oneaspect, the device of FIGS. 1A through 1E includes the combination of aconverging light source illumination system and an aperture stop. Theconverging light source illumination system operates to direct asubstantial amount of light through a small diameter opening while theaperture stop operates to block glare attributable to light rays beingreflected from outer eye structures.

[0029] As best seen by FIG. 1A, the illumination system operates togenerate illumination light rays which converge at an apex 34 anddiverge thereafter. An eye viewing device having a converging light rayillumination system is positioned in an operative position relative to apatient when substantially a maximum amount of incident light enters eye11 through pupil 12. In the device of FIGS. 1A-1E, an operative positionis achieved when apex 34 of the cone of light generated by theillumination system is positioned at about a pupil 12 of a patient. Witha converging light ray illumination system, a substantial amount ofillumination light enters a small diametered pupil and at the same timeilluminates a wide retinal field. A converging light ray illuminationsystem can be provided by the combination of a light source 14 andobjective lens 16 positioned forward of the light source 14 forconverging light rays emanating from source 14. With a converging lightsource illumination system, a much higher percentage of incident lightrays enter pupil 12 to illuminate retina 19 than are reflected off outereye structures 17 and 21. Because there is little wasted incident light,a converging light ray illumination system reduces the electrical inputpower consumption of the illumination system. Because a relativelysmaller amount of incident light reflects off outer eye structures suchas iris 17 and sclera 21, there is less unwanted light received by theimaging system.

[0030] Light source 14 can be a light generating light source, such as afilament-based lamp, an arc lamp, a fiber optic light source or a solidstate light source. However, with presently available technology, lightgenerating light sources are sufficiently large that they introducepackaging problems. Therefore, a preferred light source for the eyeviewing device is the light source described with reference to FIG. 2.In the embodiment of FIG. 2, light source 14 is provided by a reflectiveelement such as a mirror, which operates in association with alight-generating light source 18, such as a lamp, and a condenser lens20 which converges light from light source 18 onto mirror 14.

[0031] Aspects of the imaging system of the device will now be describedwith reference mainly to FIG. 1B. The imaging system of the deviceincludes objective lens 16, imaging lens 22, and an eyepiece lens 24. Aretinal image focal plane 26 is produced intermediate objective lens 16and imaging lens 22, while an eyepiece focal plane 28 is producedintermediate imaging lens 22 and eyepiece lens 24. The imaging systemfurther includes an imaging axis 30 on which lenses 16, 22, and 24 aresubstantially centered. In all references herein, the term “lens” canrefer to a single optical element or a plurality of optical elementsfunctioning together, while an operative position has been definedherein as the position at which substantially a maximum amount ofincident light rays enter eye 11 through pupil 12. An operative positioncan also be defined as the position at which a patient's pupil isconjugate to aperture stop 32.

[0032] The retinal image light rays crossing retinal focal plane 26consist of light rays that enter eye 11 through pupil 12 and which arereflected from retina 19 through pupil 12. Since small undilated pupilstend to inhibit the transmission of both incident light into an eye andreflected retinal image light out of the eye, retinal images viewedthrough undilated pupils are readily obscured by glare (which isespecially prevalent when retinas are viewed through undilated pupilssince incident light is more likely to be reflected from highlyreflected outer eye structures). In addition to glare attributable tolight being reflected from outer eye structures, retinal images can beobscured by glare attributable to other sources such as light that isreflected from a patient's cornea (corneal glare) and light that isreflected from a component of the eye viewing device such as a lens ofthe device (internal glare).

[0033] To the end that the device is well adapted for viewing retinalimages through an undilated pupil, device 10 preferably includesfeatures which operate to reduce such glare, and in so doing reduce thepercentage of received light rays not corresponding to a retinal imagerelative to the percentage of received light rays corresponding to aretinal image.

[0034] One feature which operates to reduce the percentage of light raysnot corresponding to the retinal image is the feature of converginglight illumination, described above. In a converging light illuminationsystem, a relatively high percentage of light enters eye 11 throughpupil 12, and a relatively low percentage of light is reflected fromouter eye structures 17 and 21 as seen in FIG. 1A. Other features whichmay be incorporated to increase the percentage of retinal image formingreceived light relative to unwanted light are described hereinbelow.

[0035] In the device of FIG. 1B, an aperture stop 32 is positionedforward of imaging lens 22 to block unwanted light. Aperture stop 32should be positioned substantially coaxially with imaging axis 30 andsubstantially conjugate to a patient's pupil 12 when in an operativeposition in relation to device 10. Positioning of aperture stop 32substantially coaxial with imaging axis 30 encourages substantially amaximum amount of useful receive imaging light to be admitted throughimaging lens 22 without also admitting glare light that originatesradially outside the patient's pupil 12. By positioning aperture stop 32so that it is substantially conjugate to a pupil, aperture stop 32operates to block light reflected from outer eye structures 17 and 21.Because the apex 34 of the cone of light generated by illuminationsystem is substantially conjugate to a patient's pupil for positioningthe device in an operative position, and because the preferred positionof aperture stop is also one that is conjugate to the pupil, then thepreferred position of aperture stop 32 in a device made in accordancewith FIGS. 1A-1E can be described as one that is substantially conjugateto the apex of the cone of light generated by the illumination system.

[0036] For optimal blocking of unwanted received light, aperture 33 ofaperture stop 32 should be sized in accordance with the diameter of thepupil through which a retina is viewed. The diameter of an undilatedpupil is about 2 mm. Accordingly, for optimally configuring device 10for viewing a retina through an undilated pupil, aperture 33 should besized to correspond to a patient pupil diameter of about 2 mm. Theresulting diameter of aperture 33 is determined by multiplying the pupildiameter by the magnification of the pupil in the plane of the aperturestop 32. This same principle can be applied to optimize the instrumentdesign for other pupil sizes, larger and smaller.

[0037] In addition to reducing glare and improving image quality whendevice 10 is in an operative position, aperture stop 32 reduces glareand improves image quality prior to the device being moved into anoperative position. FIGS. 1C and 1D illustrate illumination light raysexiting the device and reflecting off the eye as they are received in aviewing system of device 10 during entry of the device into an eye(during the process of moving the device into an operative position).FIG. 1C illustrates incident light rays generated by device 10 when thedevice is at a distance away from an operative position, while FIG. 1Dillustrates received reflected light rays of a device positioned awayfrom an operative position. It is seen that when the device is away froman operative position, then light rays generated by the illuminationsystem strike eye 11 in a diverged state (apex 34 of the cone of lightis positioned forward of pupil 12). Thus, a relatively small percentageof incident rays enter an eye through pupil 12 and a relatively highpercentage light rays are reflected from the highly reflective outersurfaces of eye structures such as iris 17 and sclera 21. Light raysreflected from outer eye structures 17 and 21 tend to be reflected at anangle with respect to imaging axis 30. The curved surface of eye 11assures that reflected light rays are reflected at an angle with respectto axis 30. When device 10 is a substantial distance away from anoperative position many light rays reflected from eye 11 during entry ofthe device are reflected out of the viewing system entirely. Themajority of light rays that are received in the viewing system areblocked by aperture stop 32. Only a small percentage of light rays suchas rays 37 pass through aperture 33. Light rays that pass throughaperture 33 consist of rays that originated as incident light raysdirected substantially along axis 30 and that passed through pupil 12 toretina 19. Thus, during entry of device 10 into eye 11, it can be seenthat aperture stop 32 tends to block unwanted light and to pass lightcorresponding to a retinal image.

[0038] It will be seen that without aperture stop 32, a substantialmajority of light rays transmitted to eyepiece focal plane 28 duringentry would be light rays reflected from outer eye structures 17 and 21.Thus, the image received at eyepiece focal plane 28 would be heavilyobscured by glare. With aperture stop 32 the substantial majority oflight rays received at eyepiece focal plane correspond to retina 19.During entry into the eye, the user will see a small field image of theretina, known as the “red reflex” which helps an operator move thedevice into an operative position without significant glare. Bymaintaining the retinal image spot near the center of eyepiece focalplane 28 and moving the device toward an eye 11, an operative positioncan easily be achieved.

[0039] Additional glare or unwanted light reducing features may beincorporated in the device. As is shown in FIGS. 1A-1E, light source 14may be positioned just forward of aperture stop 32 outside of theboundary between received and blocked light and off-axis with respect toimaging axis 30 of device 10. Positioning light source forward ofaperture stop 32, outside of the boundary between received and blockedlight defined by aperture 33, assures that light source 14 has noobscuring effect on the viewed image and assures maximum imagebrightness in the user's eye. Positioning light source 14 off-axis alsoreduces both internal and corneal glare. By positioning light sourceoff-axis, incident light that is reflected off of lens 16 or off ofcornea 15 directed at an angle with respect to axis 30 and, therefore,away from the optical receive path.

[0040] Glare may be further reduced by shaping the first surface 23 ofobjective lens 16 so that first surface 23 is curved and substantiallyconcentric with center of aperture 33 as seen by the embodiment of FIG.1E. This assures that light that is reflected from surface 23 isreflected to a point equal to and opposite light source 14 with respectto imaging axis 30. If light source 14 is positioned outside of boundarydividing blocked and received light defined by aperture 33, theconcentric curved first surface 23 assures that internal glare resultingfrom light being reflected from surface 23 is blocked by aperture stop32.

[0041] In addition to the above features, reducing unwanted receivedlight, glare can be reduced by disposing linear polarizers in theimaging and illumination paths in a crossed configuration.

[0042] An alternative embodiment of the invention is described withreference to FIGS. 3A-3C. In the embodiment shown in FIGS. 3A-3C, lightsource 14 is disposed directly in the field of view in a highlydefocused position in relation to focal planes 26 and 28. By disposinglight source 14 on imaging axis 30, light source 14 provides formaximally efficient illumination of a retina 19. Positioning the lightsource off-axis as is shown by light source 14 results in less-thanmaximally efficient retinal illumination, but also reduces glare forreasons that have been discussed herein.

[0043] Light source 14 in the embodiment of FIGS. 3A-3C should bepositioned in a highly defocused position in relation to any image planeof the eye viewing device conjugate to a patient's retina 19 in anoperative position in relation to device 10. As shown in the imagingsystem diagrams of FIGS. 3A-3C, a highly defocused position for source14 in relation to an image focal plane conjugate to a retina is providedby disposing source 14 intermediate retinal focal plane 26 and imaginglens 22. In general, source 14 becomes less in focus at any planeconjugate to and including eyepiece focal plane 28 as the source ismoved toward imaging lens 22 and away from retinal focal plane 26.Preferably, source 14 is positioned as close as is physically possibleto lens 22.

[0044] Corneal glare can be reduced in the embodiment of FIGS. 3A-3C ifsource 14 is disposed in device 10 in a position that is conjugate tothe surface of a cornea when the device is in an operative position inrelation to a patient. If light source 14 is positioned conjugate tocornea 15, many light rays which do happen to be reflected from cornea15 are imaged directly onto light source 14. If light source 14 isprovided by a reflective element as shown, these light rays correspondto a cornea image and are blocked before reaching eyepiece focal plane28, thereby reducing corneal glare.

[0045] In a specific example of an eye viewing device designed accordingto the general configuration described with reference to FIGS. 1A-1E and3A-3C, the objective lens 16 may be provided by a lens system having afocal length of about 25 mm, and a back focal length of about one-halfthe focal length. The eye viewing device may be configured so that thelens surface closest to the patient in the objective lens system ispositioned about 25 mm from a patient's cornea when in an operativeposition. The objective lens system accepts parallel or nearly parallellight from a patient's eye and focuses the light to an internal imagelocated at or near the back focal plane 20 of the objective. Theobjective lens system may have a diameter of about 25 mm. Imaging lens22, meanwhile, may be provided by a lens system having a focal length ofabout 25 mm, a back focal length of about 18 mm and a clear aperture ofabout 20 mm. The imaging lens may project an internal image from theobjective focal plane 26 to eyepiece focal plane 28 at a magnificationof about 0.6×. Eyepiece focal plane 28 may have an aperture of about 8mm in diameter, corresponding to the focal plane diameter of a typical20× eyepiece. The axial length from objective lens 16 to eyepiece focalplane 28 may be about 160 mm. In the illumination system described withreference to FIG. 3C, condenser lens 20 may be provided by a condensersystem having a numerical aperture of about 0.2 to 0.4, working at amagnification of about 1× to 2×, with a focal length of about 9 mm. Inthe embodiment of FIGS. 1A-1E, aperture stop 32 may be positionedsubstantially normal to axis 30 and approximately halfway between themost rearward point of light source 14 and the most forward point ofimaging lens 16. Aperture stop 32 may have an aperture diameter of about416 mm.

[0046] An alternative optical configuration for the eye viewing deviceof FIGS. 3A-3C having a defocused light source is described withreference to FIG. 4. In the eye viewing device of FIG. 4, light source14 is disposed forward of objective lens 16 and imaging lens 22 isdeleted. Light source 14 is disposed in a highly defocused position inrelation to retinal focal plane 26 by disposing light source 14 inproximity with objective lens 16. In the embodiment of FIG. 4, objectivelens 16 does not form part of the optical illumination system. Instead,illumination light rays which converge at a cornea 15 and diverge towarda retina 19 are formed by disposing condenser lens 20 in relationshipwith light source mirror 14 such that light rays reflected from themirror converge after being reflected. Further with reference to theembodiment of FIG. 4, eyepiece lens 24 may optionally be removed andreplaced with image sensor 52, such as a CCD image sensor, which ispositioned on retinal focal plane 26. A processor system (not shown) incommunication with sensor 52, can be configured to capture image signalsgenerated by sensor 52, process such signals, and if desirable,electronically reverse or magnify any captured images to accomplish thefunction provided optically by imaging lens 22 of the eye viewing deviceof FIGS. 1A-3C.

[0047] The conventional lenses in the systems described hereinabove canbe replaced with similarly functioning optical elements such asdiffractive lenses, binary gratings, phase filters, holographic opticalelements (HOE), gradient-index lenses, and hybrid optical elements.

[0048] The invention can be adapted to provide binocular viewing as isillustrated by the embodiments of FIG. 5. As seen in FIG. 5, a binoculareye viewing device according to the invention typically includes acollimating optical element 70 for collimating light rays of the imagingpath, and separating optics 72 for splitting light rays transmitted bycollimating optics 70 into two separate imaging paths 74A and 74B.Separating optics 72 typically include a combination of such opticalelements as prisms and/or mirrors. Continuing with reference to FIG. 5,binocular eye viewing device 10″ may further include orientation optics76 disposed in each binocular imaging path 74A, 74B for setting theorientation of images transmitted by separating optics as is necessary.Orientation optics 76 may include such optical elements as prism and/ormirror optical elements. Binocular eye viewing device 10″ may furtherinclude decollimation optics 78 and eyepiece optics 80 disposed in eachimaging path 74A and 74B. Each eyepiece optics 80 collimates light sothat images can be perceived by a viewer. The eye tubes (not shown) ofeyepiece optics 80 may be arranged in an orientation slightly divergingtoward a viewer's eyes to approximate the direct viewing condition of atarget by a pair of eyes.

[0049] Several functional aspects of the invention have been described.Certain additional features which may be incorporated in physicalembodiments of the invention will now be described in detail.

[0050] Shown in FIG. 6 is a physical schematic diagram of an embodimentof the invention which can be reconfigured for optimizing variousfunctional aspects of the eye viewing device. In the embodiment of FIG.6, housing 44 of eye viewing device 10 includes lens holders 60, 61, 62and 66 and replaceable lens modules 40, 41, 42 and 46 replaceablyreceived in their respective holders. As will be explained hereinbelow,replacing a certain lens module or a grouping of lens modules changesfunctional aspects of the eye viewing device enabling the ophthalmoscopeto be optimized for a specific intended use.

[0051] For example, with reference to FIGS. 1A-1E, and 3A-3C,it is seenthat the area of retina 19 that is illuminated by the illuminationsystem depends on the diameter and optical power of objective lens 16and on the magnification selected for the lens at the operative positionof the eye viewing device. This area corresponds to the angle a as shownin FIGS. 1A and 3C. The field of view of the imaging system, meanwhile,also depends on the diameter and optical power of objective lens 16 andon the magnification of the lens at the operative position of the eyeviewing device.

[0052] It is desirable that eye viewing device 10 images a wide field ofview. While a wide field of view and illumination angle, α, are highlydesirable for an accurate and efficient diagnosis of various problems, asmaller field of view and illumination angle are desirable for ease ofuse. As the angle of illumination, a, becomes less steep, illuminationlight rays are more easily directed into an eye through a pupil, so thatentry into an eye is easier. This is because as the illumination angle,α, becomes less steep, light rays from source 14 can be directed throughpupil 12 over a greater range of cornea-to-lens distances. Accordingly,in view of the above, it would be beneficial to provide an eye viewingdevice which could be configured either for optimized field of view oroptimized ease of use.

[0053] In a preferred embodiment, the imaging system of device 10 imagesa field that is wholly contained within the area of a retina that isilluminated by the illumination system. Most preferably the area of theretina that is imaged by the imaging system is about 15 percent to 30percent larger than the area that is illuminated. This feature providesimproved orientation of a viewed field and reduces alignmentconsiderations between illumination and viewing.

[0054] A possible embodiment of reconfigurable eye viewing deviceaccording to the invention is described with reference to the physicalschematic diagram of FIG. 6. This particular physical layout diagramincludes first and second lens modules 40 and 41. First lens module 40includes objective lens 16, while second lens module 41 includes imaginglens 22. While the field of view and illumination angle depend mainly onthe sizing, optical power, and magnification selected for objective lens16, imaging lens 22 will normally be replaced along with lens 16, sincethe sizing and optical power of lens 16 are coordinated with those oflens 22. The housing 44 and lens modules 40, 41 are complementarilydesigned so that the modular lens modules can be manually removed andreplaced from housing 44 while maintaining a common eyepiece focal plane28. In a reconfigurable eye viewing device, a first set of lens modulescan be provided to configure the eye viewing device for imaging a widefield of view, while a second set of modules can provide a reduced fieldof view (but with increased magnification), making the instrument easierto maneuver into an operative position. Such a device can be made easierto use simply by replacing the first set of lens modules with the secondset of lens modules.

[0055] To complement the change in field of view accomplished bychanging the first and second lens modules, the illumination condensersystem may also be changed in a modular fashion to optimize theillumination characteristics to suit the user's needs. In all condensersystems with a given condenser size, the ability to collect the lightfrom a light generating light source is balanced with the angle at whichthe light can be transmitted and the magnification at which the image ofthe light generating light source is projected. The lenses inside theillumination lens module 42 can be selected such that the illuminationsystem matches the illumination numerical aperture of the givenobjective module 40.

[0056] In a further alternate embodiment, the invention can be adaptedto capture electronic images representing an imaged retina. One suchembodiment is described with reference to FIG. 6. In FIG. 6, an eyeviewing device 10 is shown that can be reconfigured for electronic imagecapture. FIG. 6 shows an eye viewing device adapted so that eyepiecemodule 46 can be replaced with a video module 50. It is seen that eyeviewing device 10 normally includes an eyepiece module 46 having aneyepiece lens 24 which collimates imaging light rays so that a retinalimage can be viewed by a user. Eyepiece 46 can be replaced with videomodule 50 which includes certain components that configure the eyeviewing device for video capture. In particular, a video module 50 maycontain an image sensor 52, such as a CCD image sensor, which is in anoperative position in relation to the imaging system when the videomodule is installed in holder 66. The image sensor 52 is in electricalcommunication with a processor system 54 which may be programmed tocontrol image sensor 52 and to capture and, possibly to store image datagenerated by and received from image sensor 52. While processor system54 is shown as being disposed in video module 50, it is understood thatprocessor system 54 could be disposed external to video module 50. Thevideo module 50 may further be in communication with an external displayscreen and/or an external processing system via cable 56, for example,so that video images captured by image sensor can be displayed orotherwise output, and possibly archived.

[0057] Video module 50 can be designed so that image sensor 52 lies oneyepiece focal plane 28 when module 50 is in an operative position inholder 66. It is seen that an eye viewing device of the invention can beconfigured for video capture by replacing eyepiece module 46 with avideo module 50 without adding or replacing additional lenses of theimaging system. Alternative sized imagers may also be used, with theaddition of image resizing lenses. Such a configuration shifts thelocation of focal plane 28.

[0058] While the present invention has been particularly shown anddescribed with reference to the preferred mode as illustrated in thedrawings, it will be understood by one skilled in the art that variouschanges in detail may be effected therein without departing from thespirit and scope of the invention as defined by the claims.

What is claimed is:
 1. An eye viewing device comprising: an imagingaxis; an aperture stop disposed about said imaging axis; and anillumination system generating illumination lighting rays converging atan apex, wherein said illumination system includes an objective lensshaping illumination light rays, wherein said imaging axis intersectssaid objective lens, and wherein said aperture stop is disposedsubstantially conjugate to said apex.
 2. The device of claim 1, whereinsaid aperture stop is disposed substantially coaxial relative to saidimaging axis.
 3. The device of claim 1, wherein said aperture stop isdisposed in a position so that said aperture stop is in a position thatis substantially conjugate to a pupil of said eye when said illuminationsystem projects substantially a maximum amount of light through a pupilof said eye.
 4. The device of claim 1, wherein said objective lens isadapted to converge said light rays.
 5. The device of claim 1, whereinsaid imaging axis is unfolded.
 6. An eye viewing device having a patientend and an observer end, said device comprising: a housing; anillumination system generating illumination light rays for illuminatinga structure of an eye, said illumination system comprising an objectivelens and a light source; an imaging system having an imaging axisintersecting said objective lens; and an aperture stop disposed aboutsaid imaging axis, wherein said objective lens and said light source aredisposed in said housing.
 7. The device of claim 6, wherein saidaperture stop is disposed substantially coaxially relative to saidimaging axis.
 8. The device of claim 6, wherein said aperture stop issized to substantially correspond to a size of a pupil.
 9. The device ofclaim 6, wherein said illumination system generates converging lightconverging in an apex.
 10. The device of claim 6, wherein saidillumination system generates converging light converging in an apex,and wherein said aperture stop is disposed substantially conjugate tosaid apex.
 11. The device of claim 6, wherein sad imaging axis isunfolded.
 12. The device of claim 6, wherein said aperture stop isdisposed in a position so that said aperture stop is in a position thatis substantially conjugate to a pupil of said eye when said illuminationsystem projects substantially a maximum amount of light through a pupilof said eye.
 13. The device of claim 6, wherein said device comprisesoptics disposed in said housing for developing a noninverted image of aneye structure.
 14. An eye viewing device for viewing an eye having apupil, said device having a patient end and an observer end, said devicecomprising: an illumination system generating illumination light raysfor illumination a structure of an eye, said illumination systemcomprising an objective lens, an imaging system having an imaging axisintersecting said objective lens; and an aperture stop disposed aboutsaid imaging axis, wherein said aperture stop is positioned in saiddevice relative to said illumination system so that said aperture stopis substantially conjugate to said pupil when said device is in anoperative opposition in relation to said eye.
 15. The device of claim14, wherein said aperture stop is disposed substantially coaxiallyrelative to said imaging axis.
 16. The device of claim 14, wherein saidaperture stop is sized to substantially correspond to a size of a pupil.17. The device of claim 14, wherein said illumination system generatesconverging light converging in an apex.
 18. The device of claim 14,wherein said illumination system generates converging light convergingin an apex, and wherein said aperture stop is disposed substantiallyconjugate to said apex.
 19. The device of claim 14, wherein said imagingaxis is unfolded.